Method of forming symmetric nozzles in an inkjet printhead

ABSTRACT

A method of forming nozzles in an inkjet printhead including forming ink inlets in a first surface of a substrate, polishing a second surface of the substrate after the forming of the ink inlets, and forming ink outlets in the second surface of the substrate after the polishing of the second surface, the ink outlets communicating with the ink inlets.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an inkjet printhead. More particularly, the present invention relates to a method of accurately forming symmetric nozzles in an inkjet printhead.

2. Description of the Related Art

In general, an inkjet printhead is a device for printing a color image on a surface of an object, e.g., a print medium, by ejecting droplets of ink at a desired location on the object. Inkjet printheads may be classified according to the method by which ink is ejected, which includes thermal inkjet printheads and piezoelectric inkjet printheads.

In the thermal inkjet printhead, ink is quickly heated by a heater, formed of a heating element, when a pulse-type current is applied to the heater. As the ink is heated, it boils to generate bubbles. The bubbles expand and apply pressure to ink filled in an ink chamber, thereby ejecting the ink out of the ink chamber through a nozzle in the form of droplets.

In the piezoelectric inkjet printhead, a piezoelectric material is used to generate pressure through a shape transformation of the piezoelectric material, thereby ejecting the ink out of an ink chamber. FIG. 1 illustrates a schematic cross-sectional view of a conventional piezoelectric inkjet printhead. Referring to FIG. 1, a passage plate 20 may be provided with an ink passage, which may include a manifold 23, a plurality of restrictors 22 and a plurality of pressure chambers 21. A nozzle plate 10 may be provided and may include a plurality of nozzles 12 corresponding to the plurality of pressure chambers 21. Piezoelectric actuators 40 may be disposed on the passage plate 20.

The manifold 23 functions to dispense the ink from an ink storage region (not illustrated) to the plurality of pressure chambers 21. The restrictors 22 function as passages through which ink is introduced from the manifold 23 to the pressure chambers 21. The pressure chambers 21 store the ink that is to be ejected, and may be arranged on one or both sides of the manifold 23. The pressure chambers 21 vary in their volumes as the piezoelectric actuators 40 are driven, thereby generating the pressure variations that are used to eject ink through the nozzles 12 and to draw ink from the manifold 23. A portion of the passage plate 20 that defines a top wall of each pressure chamber 21 is designed to function as a vibration plate 24 that is deformed by the corresponding piezoelectric actuator 40.

The piezoelectric actuator 40 may include a lower electrode 41 disposed on the passage plate 20, a piezoelectric layer 42 disposed on the lower electrode 41 and an upper electrode 43 disposed on the piezoelectric layer 42. An insulating layer 31 may be disposed between the lower electrode 41 and the passage plate 20. The insulating layer 31 may be, e.g., a silicon oxide layer. The lower electrode 41 may be formed on an overall top surface of the insulating layer 31 to function as a common electrode. The piezoelectric layer 42 is formed on the lower electrode 41 so that it can be located above the corresponding pressure chamber 21. The upper electrode 43 is formed on the piezoelectric layer 42 to function as a driving electrode applying voltage to the piezoelectric layer 42.

In an inkjet printhead having the above-described structure, a nozzle for ejecting ink may be formed using a conventional method, which is illustrated in FIGS. 2A-2E. Referring to FIG. 2A, a silicon substrate 10 may be prepared as a nozzle plate. The thickness of the silicon substrate 10 may be, e.g., about 540 μm. Referring to FIG. 2B, the silicon substrate 10 may be reduced in thickness to, e.g., about 160 μm using, e.g., a chemical mechanical polish (CMP).

Referring to FIG. 2C, a first silicon oxide layer 13 and a second silicon oxide layer 14 may be formed on a top surface and a bottom surface of the silicon substrate 10, respectively. The first silicon oxide layer 13 may be patterned to form first apertures 15, and portions of the top surface of the silicon substrate 10 exposed through the first apertures 15 may be etched to form ink inlets 12 a, which correspond to nozzles 12. The top surface of the silicon substrate 10 may be anisotropically wet etched to form the ink inlets 12 a, and the ink inlets 12 a may have inverted pyramid shapes.

Referring to FIG. 2D, the second silicon oxide layer 14 formed on the bottom surface of the silicon substrate 10 may be patterned to form second apertures 16, and portions of the bottom surface of the silicon substrate 10 exposed through the second apertures 16 may be dry etched to form ink outlets 12 b, which communicate with the ink inlets 12 a.

Referring to FIG. 2E, the first and second silicon oxide layers 13 and 14 may be removed. Thus, nozzles 12 having the ink inlets 12 a and the ink outlets 12 b may be formed through the silicon substrate 10.

Asymmetric nozzles 12 are often formed using this conventional method of forming nozzles, as illustrated in FIGS. 3A and 3B. In particular, the four edges of the ink inlet 12 a may not be uniformly etched when the top surface of the silicon substrate 10 is wet etched through the first apertures 15 (see FIG. 2C). This may arise due to the generation of defects in the crystal structure of the silicon substrate by mechanical impact on the silicon substrate 10 during CMP, before the ink inlets 12 a are formed (see FIG. 2B), thus leading to non-uniform etching of the ink inlet 12 a.

When the nozzles 12 are asymmetric, ink droplets D ejected from the nozzle 12 may not travel straight out of the nozzle. Thus, the ink droplets D may not impinge on the target object at the desired location. Irregularities in the direction of travel of the ink droplets D may result in significant deviations from the desired locations (see FIG. 5A). In addition, the volumes and the ejection speeds of the ink droplets D ejected from the nozzles 12 may be irregular, thereby further deteriorating print quality.

SUMMARY OF THE INVENTION

The present invention is therefore directed to a method of accurately forming symmetric nozzles in an inkjet printhead, which substantially overcomes one or more of the problems due to the limitations and disadvantages of the related art.

It is therefore a feature of an embodiment of the present invention to provide a method of forming nozzles in an inkjet printhead whereby symmetric nozzles can be accurately formed regardless of the generation of defects caused by a CMP process.

At least one of the above and other features and advantages of the present invention may be realized by providing a method of forming nozzles in an inkjet printhead including forming ink inlets in a first surface of a substrate, polishing a second surface of the substrate after the forming of the ink inlets, and forming ink outlets in the second surface of the substrate after the polishing of the second surface, the ink outlets communicating with the ink inlets.

Each ink outlet may be formed directly opposite a corresponding ink inlet. The forming of the ink inlets may include removing a first portion of the substrate so as to partially penetrate the substrate, and the forming of the ink outlets may include removing a second portion of the substrate opposite the first portion, so as to completely penetrate the substrate.

The forming of the ink inlets may include forming a first layer on the first surface of the substrate, forming first apertures through the first layer by patterning the first layer, the first apertures exposing portions of the first surface of the substrate, and etching the first surface of the substrate exposed through the first apertures. The method may further include removing the first layer after the forming of the ink inlets and before the polishing of the second surface of the substrate. The method may further include removing the first layer after the polishing of the second surface of the substrate.

The substrate may be a silicon substrate, and the first layer may be a silicon oxide layer. The ink inlets may be formed to have an inverted pyramid shape. The substrate may be a single crystal substrate, and the forming of the ink inlets may include an anisotropic etch. The substrate may be a single crystal silicon substrate. The anisotropic etch may be a wet etch using tetramethyl ammonium hydroxide (TMAH). The polishing of the second surface of the substrate may include using chemical mechanical polishing (CMP).

The forming of the ink outlets may include forming a second layer on the second surface of the substrate, forming second apertures through the second layer by patterning the second layer, the second apertures exposing portions of the second surface of the substrate, forming the ink outlets by etching the second surface of the substrate exposed through the second apertures, and removing the second layer. The substrate may be a silicon substrate, and the second layer may be a silicon oxide layer. The forming of the ink outlets may include forming a second layer on the first and second surfaces of the substrate, forming an aperture in the second layer on the second surface of the substrate, and removing a portion of the second surface of the substrate so as to penetrate the substrate and the second layer on the first surface of the substrate. The forming of the ink outlets may include a dry etch. The dry etch may be a reactive ion etch (RIE) using induced coupled plasma (ICP).

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:

FIG. 1 illustrates a schematic cross-sectional view of a conventional piezoelectric inkjet printhead;

FIGS. 2A-2E illustrate cross-sectional views of stages in a conventional method of forming nozzles;

FIGS. 3A and 3B illustrate a plan view and a cross-sectional view, respectively, of a conventionally formed nozzle;

FIGS. 4A-4I illustrate cross-sectional views of stages in a method of forming a nozzle according to an embodiment of the present invention;

FIG. 5A illustrates a graph of performance of a printhead manufactured according to the conventional method; and

FIG. 5B illustrates a graph of performance of a printhead manufactured according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Korean Patent Application No. 10-2005-0001545, filed on Jan. 7, 2005, in the Korean Intellectual Property Office, and entitled: “Method of Forming Symmetric Nozzles in Inkjet Printhead,” is incorporated by reference herein in its entirety.

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the figures, the dimensions of layers and regions are exaggerated for clarity of illustration. It will also be understood that when a layer is referred to as being “on” another layer or substrate, it can be directly on the other layer or substrate, or intervening layers may also be present. Further, it will be understood that when a layer is referred to as being “under” another layer, it can be directly under, and one or more intervening layers may also be present. In addition, it will also be understood that when a layer is referred to as being “between” two layers, it can be the only layer between the two layers, or one or more intervening layers may also be present. Like reference numerals refer to like elements throughout.

According to the present invention, CMP may be used to thin a nozzle substrate, and nozzles formed therein may be accurately formed regardless of whether the CMP induces defects in the substrate. In particular, in contrast to the conventional method, ink inlets may be formed in a first surface of the substrate before CMP, such that mechanical impacts due to CMP do not affect the substrate until after formation of the ink inlets. Thus, where the substrate is a crystal substrate, the effects of defects in the crystal structure of the substrate, caused by the CMP, on the formation of the ink inlets may be reduced or eliminated. Accordingly, where the ink inlets are formed in a crystal substrate through anisotropic etch, accurately and symmetrically formed ink inlets may be achieved.

FIGS. 4A-4I illustrate cross-sectional views of stages in a method of forming a nozzle according to an embodiment of the present invention. Referring to FIG. 4A, a substrate 110 may be used to form a nozzle portion of a printhead. The substrate 110 may be, e.g., a silicon substrate. The substrate 110 may be a single crystal wafer, e.g., a single crystal silicon wafer of the type used to manufacture semiconductor devices, which may be easily obtained from wafer manufacturers. The thickness of the substrate 110 may be, for example, about 540 μm.

As illustrated in FIGS. 4A-4E, a first surface of the substrate 110, e.g., the top surface as illustrated, may have ink inlets 121 formed therein. The ink inlets 121 may be formed by, e.g., removing a portion of the substrate 110 from the first surface so as to partially, but not completely, penetrate the substrate 110. The ink inlets 121 may be formed by, e.g., an etching process.

In detail, referring to FIG. 4A, a first layer 111 may be formed on the first surface of the substrate 110. The first layer 111 may be, e.g., a silicon oxide layer. Where the substrate 110 is a silicon substrate, the substrate 110 may be put into an oxidization furnace to wet-oxidize or dry-oxidize the first surface of the substrate 110, thereby forming the first layer 111 as a silicon oxide layer, or the first layer 111 may be formed using chemical vapor deposition (CVD). Another first layer 111′ may be formed on the second surface of the substrate 110, e.g., the bottom surface as illustrated.

Referring to FIG. 4B, a photoresist PR may be spread onto the surface of the first layer 111 formed on the first surface of the substrate 110. The photoresist PR may then be patterned using, e.g., typical processes such as exposure and development.

Referring to FIG. 4C, the first layer 111 formed on the first surface of the substrate 110 may be partially etched using the patterned PR as an etch mask to form first apertures 113, which are located where ink inlets 121 are to be formed. The photoresist PR may then be removed. Thus, portions of the first surface of the substrate 110 may be exposed through the first apertures 113.

Referring to FIG. 4D, the exposed portions of the first surface of the substrate 110 may be partially removed to form ink inlets 121. In particular, the first layer 111 may be used as a mask. Where the substrate 110 is a single crystal substrate, the exposed portions may be partially removed through an anisotropic etching process. For example, tetramethyl ammonium hydroxide (TMAH) may be used to obliquely etch a single crystal silicon substrate 110, due to different etching rates according to the orientation of the silicon crystal plane. The resulting ink inlets 121 may have, e.g., inverted pyramid shapes.

After forming the ink inlets 121, the first layers 111 and/or 111′ may be removed using, e.g., wet etching, dry etching, etc.

Referring to FIG. 4E, the substrate 110 may be reduced in thickness by, e.g., polishing the second surface until the substrate 110 has the desired thickness. The substrate 110 may be reduced to, e.g., about 160 μm. The second surface of the substrate 110 may be polished using CMP.

Referring to FIGS. 4F-4I, the second surface of the substrate 110 may be partially removed to form ink outlets 122 communicating with the ink inlets 121. In detail, referring to FIG. 4F, a second layer 112 may be formed on the second surface of the substrate 110. Where the substrate 110 is a silicon substrate, the second layer 112 may be, e.g., a silicon oxide layer and may be formed by, e.g., putting the substrate 110 into an oxidization furnace to wet-oxidize or dry-oxidize the second surface of the substrate 110 to form silicon oxide thereon, or the second layer 112 may be formed using, e.g., CVD. Another second layer 112′ may be formed on the first surface of the substrate 110.

Referring to FIG. 4G, the second layer 112 formed on the second surface of the substrate 100 may be patterned to form second apertures 114, which are located where ink outlets 122 are to be formed. The second layer 112 may be patterned using, e.g., the same method illustrated in FIGS. 4B and 4C.

Referring to FIG. 4H, portions of the second surface of the substrate 110 exposed through the second apertures 114 may be removed to form ink outlets 122 communicating with the ink inlets 121. The ink outlets 122 may be cylindrical and may be formed by, e.g., an etching process. The second layer 112 may be used as an etch mask. The second surface of the substrate 110 may be dry etched using reactive ion etching (RIE) using induced or inductively coupled plasma (ICP).

In forming the ink outlets 122, the second layers 112, 112′ may be formed on the second and first surfaces of the substrate, respectively. Following formation of the second apertures 114 in the second layer 112 on the second surface of the substrate 110, the ink outlets 122 may be formed by removing a portion of the second surface of the substrate 110 so as to penetrate the substrate 110 and the second layer 112′ on the first surface of the substrate 110.

Referring to FIG. 4I, the second layers 112 and 112′ may be removed using, e.g., wet or dry etching. Thus, the nozzles 120 having the ink inlets 121 and the ink outlets 122 may be formed through the substrate 110

FIG. 5A illustrates a graph of performance of a printhead manufactured according to the conventional method, and FIG. 5B illustrates a graph of performance of a printhead manufactured according to the present invention. In FIGS. 5A and 5B, L denotes nozzles arranged at a left side of a manifold, R denotes nozzles arranged at a right side of a manifold, and kHz denotes a driving frequency.

Referring to FIG. 5A, the deviations between the targeted locations on the print medium and the actual points of impact of the ink droplets are large, and the distribution of the deviations is irregular. However, according to the method of the present invention, nozzles may be formed having a higher level of performance. In particular, referring to FIG. 5B, the deviations between the targeted locations and actual points of impact are smaller, and the distribution of the deviations is more consistent, which is indicative of the symmetric nature of the nozzles formed according to the present invention. For example, the deviations of the points of impact for the conventionally manufactured nozzles analyzed in FIG. 5A include many instances where the deviation exceeds ±40 μm. In contrast, the deviations of the points of impact for the nozzles manufactured according to the present invention, illustrated in FIG. 5B, are within ±40 μm.

As described above, according to the present invention, CMP may be performed after the formation of ink inlets, and thus the resulting nozzles, more specifically, the ink inlets of the nozzles, may be accurately and symmetrically formed regardless of the generation of defects caused by the CMP. Accordingly, nozzles may be formed from which ink droplets are ejected straight, and the volume and the ejection speed of the ink droplets may be made more uniform, thereby improving printing quality.

Exemplary embodiments of the present invention have been disclosed herein, and although specific terms are employed, they are used and are to be interpreted in a generic and descriptive sense only and not for purpose of limitation. Accordingly, it will be understood by those of ordinary skill in the art that various changes in form and details may be made without departing from the spirit and scope of the present invention as set forth in the following claims. 

1. A method of forming nozzles in an inkjet printhead, comprising: forming ink inlets in a first surface of a substrate; polishing a second surface of the substrate after the forming of the ink inlets; and forming ink outlets in the second surface of the substrate after the polishing of the second surface, the ink outlets communicating with the ink inlets.
 2. The method as claimed in claim 1, wherein each ink outlet is formed directly opposite a corresponding ink inlet.
 3. The method as claimed in claim 2, where the forming of the ink inlets includes removing a first portion of the substrate so as to partially penetrate the substrate; and the forming of the ink outlets includes removing a second portion of the substrate opposite the first portion, so as to completely penetrate the substrate.
 4. The method as claimed in claim 1, wherein the forming of the ink inlets includes: forming a first layer on the first surface of the substrate; forming first apertures through the first layer by patterning the first layer, the first apertures exposing portions of the first surface of the substrate; and etching the first surface of the substrate exposed through the first apertures.
 5. The method as claimed in claim 4, further including removing the first layer after the forming of the ink inlets and before the polishing of the second surface of the substrate.
 6. The method as claimed in claim 4, further including removing the first layer after the polishing of the second surface of the substrate.
 7. The method as claimed in claim 4, wherein the substrate is a silicon substrate, and the first layer is a silicon oxide layer.
 8. The method as claimed in claim 1, wherein the ink inlets are formed to have an inverted pyramid shape.
 9. The method as claimed in claim 1, wherein the substrate is a single crystal substrate, and the forming of the ink inlets includes an anisotropic etch.
 10. The method as claimed in claim 9, wherein the substrate is a single crystal silicon substrate.
 11. The method as claimed in claim 9, wherein the anisotropic etch is a wet etch using tetramethyl ammonium hydroxide (TMAH).
 12. The method as claimed in claim 1, wherein the polishing of the second surface of the substrate includes using chemical mechanical polishing (CMP).
 13. The method as claimed in claim 1, wherein the forming of the ink outlets includes: forming a second layer on the second surface of the substrate; forming second apertures through the second layer by patterning the second layer, the second apertures exposing portions of the second surface of the substrate; forming the ink outlets by etching the second surface of the substrate exposed through the second apertures; and removing the second layer.
 14. The method as claimed in claim 13, wherein the substrate is a silicon substrate, and the second layer is a silicon oxide layer.
 15. The method as claimed in claim 1, wherein the forming of the ink outlets includes: forming a second layer on the first and second surfaces of the substrate; forming an aperture in the second layer on the second surface of the substrate; and removing a portion of the second surface of the substrate so as to penetrate the substrate and the second layer on the first surface of the substrate.
 16. The method as claimed in claim 1, wherein the forming of the ink outlets includes a dry etch.
 17. The method as claimed in claim 16, wherein the dry etch is a reactive ion etch (RIE) using induced or inductively coupled plasma (ICP). 